Scientific American, 12/26/13,
Exoplanets are almost old hat to astronomers, who by now have found more than 1,000 such worlds beyond the solar system. The next frontier is exomoons—moons orbiting alien planets—which are much smaller, fainter and harder to find. Now astronomers say they may have found an oddball system of a planet and a moon floating free in the galaxy rather than orbiting a star.
The system showed up in a study using micro lensing, which looks for the bending of starlight due to the gravitational pull of an unseen object between a star and Earth. In this case the massive object might well be a planet and a moon. But the signal is not very clear, the researchers acknowledge, and could instead represent a dim star and a lightweight planet. “An alternate star-plus-planet model fits the data almost as well” as the planet-plus-moon explanation, the scientists reported in a paper that was posted this week on the preprint site arXiv. The study has not yet been peer-reviewed.
